Synthetic ester lubricant compositions with improved ryder gear load-carrying ability

ABSTRACT

A lubricant composition comprised of a major amount of a synthetic ester oil having an inherent Ryder gear load-carrying ability of less than 2200 pounds per inch and a minor, loadcarrying improving amount of a mono-, di- or trihydrocarbyl ammonium salt of an organic carboxylic acid exhibits improved Ryder gear load-carrying ability.

United States Patent [1 1 Shaub et al.

[ SYNTHETIC ESTER LUBRICANT COMPOSITIONS WITH IMPROVED RYDER GEAR LOAD-CARRYING ABILITY [75] Inventors: Harold Shaub, New Providence;

Adolph J. Garbus, Roselle, both of [73] Assignee: Exxon Research & Engineering Co.,

Linden, NJ.

[22] Filed: Apr. 26, 1972 [21] Appl. No.: 247,742

[52] U.S. Cl 252/343; 252/34 [51] Int. Cl. Cl0m 3/18; ClOm 3/26 [58] Field of Search 252/347, 34

[56] References Cited UNITED STATES PATENTS 2,228,325 l/l94l Olin et al. 252/5l 2,344,886 3/1944 Lieber 252/427 Nov. 18, 1975 2,758,086 8/]956 Stuart el al. 252/34 X 2,911,368 l1/l959 Fowler et a! 252/34 3.203.896 8/[965 Latos et al. 252/34 X FOREIGN PATENTS OR APPLICATIONS 750,340 6/1956 United Kingdom 797,452 7/l958 United Kingdom Primary Examiner-H. Sneed Attorney, Agent, or FirmDaniel H. Hall; Byron O. Dimmick ABSTRACT A lubricant composition comprised of a major amount of a synthetic ester oil having an inherent Ryder gear load-carrying ability of less than 2200 pounds per inch and a minor, load-carrying improving amount of a mono, dior trihydrocarbyl ammonium salt of an organic carboxylic acid exhibits improved Ryder gear loadcarrying ability.

4 Claims, No Drawings SYNTHETIC ESTER LUBRICANT COMPOSITIONS WITH IMPROVED RYDER GEAR LOAD-CARRYING ABILITY FIELD OF THE INVENTION This invention relates to synthetic ester based lubricant compositions containing hydrocarbyl ammonium salts of organic carboxylic acids and which exhibit improved Ryder gear load-carrying abilities.

DESCRIPTION OF THE PRIOR ART U.S. Pat. No. 2,228,325 discloses the use of mono-, diand trialkyl ammonium salts of both carboxylic and inorganic acids in mineral oil hydrocarbon lubricant base stocks to improve load-carrying abilities.

U.S. Pat. No. 2,344,886 discloses the use in oils, in-

eluding synthetic oils, of various tetrahydrocarbyl am- SUMMARY OF THE INVENTION The present invention relates to lubricant compositions based on synthetic ester oils having inherent Ryder gear load-carrying abilities of less than 2200 pounds per inch. Thes synthetic ester oils are improved in their load-carrying abilities by the addition to them of mono-, dior trihydrocarbyl ammonium salts of organic carboxylic acids. In contrast to the disclosures of the above-noted U.S. Pat. No. 2,228,325. it has now been found that mono-, diand trihydrocarbyl ammonium salts of organic carboxylic acids can be used in synthetic as well as mineral oil lubricant base stocks. Furthermore, of the broad range of compounds disclosed in the U.S. Pat. No. 2,228,325 only specific classes are successful in imparting improved load-carrying abilities to the synthetic ester oils of this invention. While the U.S. Pat. No. 2,228,325 discloses other classes of materials which may also be useful for improving load-carrying abilities of mineral oils, the presence of chlorine or inorganic residues in such compounds makes them unsuitable for use in the synthetic ester oils of this invention because of their detrimental effects on oxidation and corrosion properties of the oil.

In contrast to the disclosure of the above-noted U.S. Pat. No. 2,344,886, the present invention comtemplates the use of mono-, diand tertiary hydrocarbyl ammonium salts which are soluble in synthetic ester base stocks. The tetrasubstituted ammonium compounds of the U.S. Pat. No. 2,344,886 generally have low solubilities in such oils.

It is particularly surprising that the ammonium salts of the present invention are able to improve the Ryder gear load-carrying ability of synthetic ester oils having inherent load-carrying abilities of less than 2200 pounds per inch since they are generally unable to improve the load-carrying ability of ester oils having greater inherent load-carrying abilities. While the latter esters have found acceptance in use for the lubrication of jet engines used to power commercial aircraft, the former type of oils are still widely used because of their low temperature properties and lesser cost.

DETAILED DESCRIPTION OF THE INVENTION Synthetic Ester Oils The synthetic lubricant base stocks used in this invention can contain a major proportion of one or more compounds having the following structural formulae:

In all the above formulae. R and R are the residues of dicarboxylic acids, e.g., HOOCR COOH. R and R are the residues of monohydric alcohols. e.g.. R OH. R and R' are the residues of monocarboxylic acids: R COOH. R and R are the glycols, e.g., HOR,OH. n is a number from I to 6 which need not necessarily be integral and, where it is fractional, represents the average of a mixture of compounds. It is preferred that the monohydric alcohols be aliphatic alcohols, or ether alcohols.

Some branching in the hydrocarbon chain of the radical R is possible. and the alcohols derived from the 0x0 synthesis discussed below may be used. Generally R has from 4 to l8 carbon atoms and can contain in certain instances oxygen atoms in the form of ether linkages. The monocarboxylic acids, R COOH, are preferably aliphatic acids and contain from I to 22 car bon atoms. The glycols are preferably members of the alkylene glycol or polyalkylene glycol series. The polyethylene glycols from dicthylenc glycol up to decaethylene glycol, or diols of the formula H(OCH CH- ),,OH where n is from 3 to 12, are useful. The molecu lar weight and structure of the esters should be such that the resulting base stock has a viscosity between I es. and 4.5 cs., preferably 2 to 4 cs.. at 210F.

The above-noted synthetic diesters can be made by the reaction of a monohydric alcohol with a diacid or by the reaction ofa monocarboxylic acid with a glycol. The monohydric alcohols, R OH, useful for making such diesters contain l to l8 carbon atoms. Typical alcohols are the following: methyl alcohol, ethyl alcohol. n-butyl alcohol, 2-ethyl hexyl alcohol. n-octyl alcohol. decyl alcohol, C Oxo alcohol and C Oxo alcohol.

A group of alcohols which can be used in preparing the synthetic esters of the present invention are the socalled "Oxo" alcohols, prepared by the well-known Oxo synthesis. This process involves the catalytic reaction of olefins with carbon monoxide and hydrogen at elevated temperatures of about 300 to 400F and pressures of about 2500 to 4000 psig to form, particularly in the presence of cobalt catalysts. aldehydes having one carbon atom more than the olefin originally used. The aldehyde is catalytically hydrogenated to the corresponding alcohol which is recovered as an overhead product by distillation of the reaction mixture. The distillation residue, i.e., the so-called Oxo-bottoms, is rich in by-product alcohols of higher molecular weight. This residue may also be employed.

While the exact compositions of all these alcohols are not known, it is well established that they are mixtures of primary alcohols, at least a substantial proportion of which is of the branched-chain type. The overhead alcohol product consists ofa mixture of such alcohols av eraging 1 carbon atom more than the olefin originally fed to the Oxo synthesis. Oxo alcohols containing in the range of about 6 to H) carbon atoms are preferred for the purposes of the present invention.

Esters having suitable properties for the purposes of this invention may be prepared from oxo alcohols produced by reacting telomers ofC and (T monooleftns in the presence of oxonation catalysts as described above. Appropriate mixtures of these monoolefins are readily available in refinery gases, and processes for their conversion into liquid telomers are well known in the art. in accordance with the most widely used of these processes. the olefms are contacted in the liquid phase with a telomerization catalyst comprising phosphoric acid supported on kieselguhr. Other similar proccesscs use as catalysts silica gel impregnated with phosphoric acid. or sulfuric acid. Friedcl-Crafts catalysts. activated clays and others. Telomerization conditions in the presence of phosphoric acid catalysts include temperatures of about 300 to 500F and pressures of about 250 to 5000 psig. The olefinic feed stocks normally contain about to 60 mol percent of propylene. about 0.5 to 50 mol percent of butylenes and from 0.l to 10 mol precent of isobutylene. the remainder being saturated hydrocarbons having 2 to 4 carbon atoms per molecule. in place of. or together with. these olefin mixturcs. the dimer and trimer of isobutylene as well as tri-. tetraand pentapropylcne may be used.

The composition and structure of C Oxo alcohols obtained from a mixture of C, olcfins of the type described above and more specifically of C olefins derived from a refinery gas stream containing propylene and mixed normal and isobutylenes are shown below:

Structure of C, Oxo alcohols prepared from 4 straight-chain olefins are used as the starting materials the alcohols obtained consist predominantly of branched-chain compounds.

The glycols employed in preparing the esters of the present invention have 2 to 18 carbon atoms and include ethylene glycol and any of the paraffinic homologues of the same containing up to 18 carbon atoms. These may include. for example. ethylene glycol. propylene glycol. neopenty glycol. pinacol. trimethylene glycol. tetramethylene glycol. pentamcthylene glycol and the like. Compounds such as diethylene glycol. triethylcnc glycol. the polyethylene glycols of the formula:

HOCH,CH,0(CH,CH,0).H wherein n is 0 to 26. and the polypropylene glycols of the general formula s is s It HOUl'H- HOhlH- HOH where either R or R is a methyl group and the other is hydrogen. and where n is 0 to 20. may be employed.

Among the monobasic acids which may be employed in the preparation of the esters of the present invention. the following may be listed as illustrative:

Acetic acid Propionic acid Butyric acid Valerie acid Caproic acid Caprylic acid Pelurgonic acid Laurie acid Palmitic acid Stearic acid Oleic acid B-Methoxypropionic acid B-Tert.-Octoxypropionic acid Oxalic acid Malonic acid Succinic acid Glutaric acid Adipic acid Pimelic acid Suberic acid Azelaic acid Sehacic acid Brassylic acid Tetracosane C -C Alkenyldicarboxylic acid suecinic acids Dicylcollic acid Carhun-alkyl derivatives of the above acids. as. c.g.. l-rncthyl adipic acid. ism schacic acid. a. a. diethyl adipic acid.

The C -C alkenylsuccinic acids listed above are prepared by condensing olefins or mixtures of olefins with maleic anhydride. Generally. the dibasic acids used to prepare the esters of this invention contain 4 to 22 carbon atoms. Preferred dibasic acids have the formula:

HOOC(CH),COOH where .r is a number of from 2 to 10.

The esters of this invention also include mixtures of the above-described esters with polyesters such as the triesters and tetraesters formed by reacting triand tetrapolyols such as trimethylol propane. pentaerythritol. trimethylol ethane. and higher trimethylol alkanes, and so forth. with a C -C normal or branched chain momoearboxylic acid or mixtures of two or more of such types of acids. These acids are exemplified by the n-butanoic acid. valeric acid. caproic acid, heptanoic acid. caprylic acid. pivalic acid. 2-ethyl hexanoic acid.

pelargonic acid. lauric acid and the like. These mixtures contain to 90 wt. '71 of the diester and have Ryder gear load-carrying abilities of less than 2200 lbs/in.

The esterification reactions employed in the production of the synthetic diand complex esters used in this invention are generally carried out under conditions known to the art. The acid and alcohol or glycol reactants are generally heated under reflux conditions with a catalyst and water entraincr such as benzene or xylene. In the reaction, acidic catalysts may be used, for example, sodium acid sulfate, sulfuric acid, paratoluene sulfonic acid, etc. Alternatively, amphoteric metal salts such as stannous oxalate may be employed. When the esterification reaction is complete. the reaction mixture is normally neutralized by washing it with a dilute alkaline solution, such as aqueous sodium hydroxide, followed by neutral water washing. After this, the ester is vacuum stripped. often under reduced pressure, to remove any water contamination, entrainer, unreacted starting materials, etc.

Complex ester base stocks may be formed by reacting a diacid with a glycol in a glycol-to-diacid molar ratio, e.g., of 0.5 to 2.0 and then reacting the intermediate product with 2 to 0.5 moles of monohydric alcohol per mole of intermediate or reacting the intermediate product with 2 to 0.5 moles of a monocarboxylic acid per mole of intermediate. Detailed descriptions for the preparation of complex esters of the above-described type appear, for example, in U.S. Pat. Nos. 3,126,344 and 3,016,353.

Hydrocarbyl/Ammonium Salts The ammonium salts used in the practice of this invention have the general formula:

wherein R is a C to C hydrocarbyl moiety, R is a C to C hydrocarbyl moiety, R and R are each a hydrogen atom or C to C hydrocarbyl moiety and said salt contains a total of 10 carbons to 40 carbons. Preferably R is an aliphatic moiety containing 8 to 18 carbon atoms, and R is preferably an aliphatic moiety containing 4 to 12 carbon atoms while R and R are hydrogen atoms.

Typical of the ammonium salts used in the present invention are:

ndodecyl ammonium caprylate n-butyl ammonium oleate isobutyl ammonium Z-ethylhexyl ammonium vnlerate diethyl ammonium stearate ocladecyl butyl etc.

The ammonium salts used in the present invention can be prepared by means well-known to those of skill in the art. for example, an amine can be reacted with an organic acid by mixing stoichiometric amounts of the two reactants in l to 4 parts by volume of solvent per part by volume of reactants at a temperature from to 210F for to 120 minutes. The salts can be recovered by distilling off the solvent at a pressure of 100 to 10 mm of Hg, at a temperature of 100 to 2 10F and recovering the product by standard means.

Alternatively. an ammonium salt of an inorganic acid such as an amine hydrochloride can be reacted in l to 4 parts of an inert solvent with a metal carboxylic acid 6 salt. Such reactions often occur under milder conditions than the aforesaid reaction.

The lubricating oil compositions of this invention contain from 0.1 to 5 wt. 7: of the ammonium salt based upon the synthetic oil base stock. preferably 0.5 to 2.5 wt. 7:. most preferably 0.5 to 1.5 wt. 72. Preferably, the compositions of the present invention are prepared by dissolving the ammonium salts in the synthetic ester base stock. This can be accomplished by heating a mixture of the two at a temperature of 150 to 220F for 10 to 60 minutes with mild agitation. Alternatively. the ammonium salt can be compounded into a concentrate. The concentrate may be comprised of 5 to 25 parts of the ammonium salt and in 95 to parts of the ester base stocks described above.

The lubricating oil compositions of this invention (which comprise a major proportion of a lubricating oil) may, in addition to the abovedescribed ammonium salts, also include minor proportions of conventional additives such as V. l. improvers or thickeners. e.g.. polymethacrylates, polyacrylates; extreme pressure agents. e.g.. dialkyl acid phosphites; oxidation inhibitois, e.g., phenothiazine; rust inhibitors; e.g., ammonium hydrocarbon sulfonate, lecithin. Span antiwear agents, e.g.. tricresyl phosphate; and the like, to obtain desired results. The ester compositions of this invention may also be employed as the lubricating oil component or one of the components of grease compositions, in which composition they may be thickened to a grease consistency with conventional thickeners such as soaps, soap-salt complexes. and the like.

The invention will be more fully understood by reference to the following examples. It is pointed out, however, that the examples are given for the purpose of illustration only and are not to be construed as limiting the scope of the present invention in any way.

EXAMPLE 1 A lubricant composition, according to the present invention, was prepared by dissolving 0.5 part by weight of n-butyl ammonium oleate in parts by weight of a C /C 0x0 alcohol adipate ester. The adipate ester was prepared by esterifying adipic acid with a mixture of C, and C Oxo alcohols wherein there were 60 molar parts of C alcohol to 40 molar parts of c alcohol. The extreme pressure properties of the lubricant composition formulated as described in Example 1 were evaluated in the Ryder gear test using the Ryder gear machine described in ASTM method D-l947. Briefly. this test subjects a set of gears lubricated by the test oil to a series of load increments under controlled conditions. The amount of tooth-face scuffing occurring at each load is measured. The percentage of toothface scuffing is plotted against the load to determine the load-carrying ability of the test oil. The load-carrying ability of the oil is defined as the tooth load, in pounds per inch of gear tooth, at which an average tooth-face scuffing at 22.5% of the tooth area has been reached.

The lubricant composition of Example 1 gave a Ryder gear load of 2294 lbs. per inch of gear tooth. In contrast. the C /C Oxo adipate base stock. by itself, gave a gear load of 1590 lbs. per inch of gear tooth. Thus, the composition of Example 1, made in accor dance with this invention, exhibited a Ryder gear loadcarrying ability that was that of the synthetic ester base stock from which it was made.

EXAMPLE 2 One hundred parts of the C IC Oxo adipate of Example l was blended with 1 part by weight of n-butyl ammonium oleate. This composition gave a Ryder gear load of 2500 lbs. per inch of gear tooth. In contrast, a composition composed of I parts of the C,,/C Oxo adipate with l part of oleic acid (a known extreme pressure agent) gave a Ryder gear load of 20l6 lbs. per inch of gear tooth. Example 2 again demonstrates that a composition prepared in accordance with this invention exhibits Ryder gear load-carrying properties better than those of either the base stock alone or the base stock formulated with an equivalent amount of a known extreme pressure agent such as oleic acid.

COMPARISON l A synthetic lubricant composition was formulated from 100 parts of a pentaerythritol dipentaerythritol ester of a mixture of aliphatic C to C carboxylic acids wherein the aliphatic acids had an average chain length of 6.6 carbons, with 1 part by weight of n-butyl ammonium oleate. This base stock is typical of the hindered polyol ester oils which have inherent Ryder gear loadcarrying abilities in excess of 2200 lbs/inch. Such base stocks generally have a 2 l 0"! viscosity in excess of 4.5 es. and no beta hydrogen in the alcoholic portion of the molecule. The load-carrying properties of this composition were evaluted in the Ryder gear test described above. This composition gave a Ryder gear load of 2966 lbs. per inch of gear tooth. In contrast. the stock by itself gave a Ryder gear load of 3000 lbs. per inch of gear tooth. This example clearly demonstrates that base stocks having a Ryder gear load in excess of 2200 lbs. are not improved in their load-carrying abilities through the use of the additives in the present invention.

EXAMPLE 3 A lubricant composition was prepared from 100 parts by weight of the C /C Oxo adipate described above containing l .0 part of n-butyl ammonium oleate.

The 347F Oxidation-Corrosion-Stability Test was carried out by blowing dry air at the rate of 50 volumes per hour through 1 volume of the lubricating composition maintained at a temperature of 347F for 72 hours. At the end of the test. the increase in viscosity and the increase in total acid number (T.A.N.) were determined. The corrosive characteristic of the lubricant was determined by immersing various weighed metal strips in the oil and measuring weight change at the end of the test. The change in weight signifies either corro- METAL WEIGHT LOSS. mg/cni copper .()2 magnesium iron --[)I aluminum silver 9% evaporation loss used oil T.A.N.

From an examination of the data in the Table, it can be seen that the composition of Example 3 had satisfactory oxidative stability.

What is claimed is:

l. A lubricant composition of improved load-carrying ability comprised of a major portion of synthetic ester oil having an inherent Ryder gear load-carrying ability of less than 2200 pounds per inch and a minor amount, in the range of 0.l to 5.0 wt. of an ammonium salt of an organic carboxylic acid, said salt having the formula R'Co,-NH*R*RR* wherein R is a C to C aliphatic hydrocarbyl moiety, R is a C aliphatic hydrocarbyl moiety. and R" and R are each a hydrogen atom.

2. A composition as claimed in claim I wherein the synthetic ester oil is of the formula R,00CR,CO0R', or rgcooapock' wherein R is the residue of a C to C dicarboxylic acid R, and R; are the residues of C to C monohydric alcohol and R and R';, are C to C residues of monocarboxylic acids.

3. A composition as claimed in claim 1 where the synthetic ester oil is a mixture of at least one diester with at least one trior tetraester.

4. A composition as claimed in claim 1 wherein the ammonium salt is N-butyl ammonium oleate and the synthetic diester oil is a diester of a dicarboxylic acid selected from the group consisting of adipic, sebacic and azelaic acids. and a C to C alcohol or mixtures thereof.

4* i i i =0 

1. A LUBRICANT COMPOSITION OF IMPROVED LOAD-CARRYING ABILITY COMPRISED OF A MAJOOR PORTION OF SYNTHETIC ESTER OIL HAVING AN INHERENT RYDER GREAR LOAD-CARRYING ABILITY OF LESS THAN 2200 POUNDS PER INCH AND A MONOR AMOUNT, IN THE RANGE OF 0.1 TO 5.0 WT. %, OF AN AMMONIUM SALT OF AN ORGANIC CARBOXYLIC ACID, SAID SALT HAVING THE FORMULA R1-COO(-) . (+)HN(-R4)(-R2)-R3 WHEREIN R1 IS A C8 TO C18 ALIPHATIC HYDROCARBYL MOIESTY, R2 IS A C1 ALIPHATIC HYDROCARBYL MOIIETY, AND R3 AND R4 ARE EACH A HYDROGEN ATOM.
 2. A composition as claimed in claim 1 wherein the synthetic ester oil is of the formula R2OOCR1COOR''2 or R3COOR1OOCR''3 wherein R1 is the residue of a C4 to C22 dicarboxylic acid R2 and R''2 are the residues of C4 to C18 monohydric alcohol and R3 and R''3 are C1 to C22 residues of monocarboxylic acids.
 3. A composition as claimed in claim 1 where the synthetic ester oil is a mixture of at least one diester with at least one tri-or tetraester.
 4. A composition as claimed in claim 1 wherein the ammonium salt is N-butyl ammonium oleate and the synthetic diester oil is a diester of a dicarboxylic acid selected from the group consisting of adipic, sebacic and azelaic acids, and a C6 to C10 alcohol or mixtures thereof. 